Sulfur- and Nitrogen-Incorporated Phenothiazine-Based Porous Organic Polymer: Selective and Efficient CO₂ Capture and Evaluation for Vacuum Swing Adsorption

Carbon capture and storage (CCS) is considered an effective strategy for reducing CO₂ emissions and addressing climate change. We report the synthesis of rigid, robust phenothiazine and 3D triptycene-containing microporous polymer (NS-TMP) possessing nitrogen and sulfur heteroatoms via a one-pot facile Friedel-Crafts reaction as an efficient microporous adsorbent for selective CO₂ capture. The incorporation of triptycene units in the NS-TMP polymer structure imparts several advantageous characteristics, including inherent microporosity, increased surface area, and enhanced thermal stability. NS-TMP exhibits significant micropore volume, a BET-specific surface area (SA_BET) of 863 m²/g, and promising thermal stability (T_d = 321 °C). Additionally, the presence of phenothiazine units containing N and S heteroatoms enhances its ability for selective CO₂ capture. NS-TMP demonstrates a strong affinity for CO₂, with a heat of adsorption (Q_st) of 35 kJ/mol, indicating an excellent CO₂ adsorption capacity, significantly influenced by the micropore volume. The selectivity for CO₂/N₂ and CO₂ over CH₄ for NS-TMP was estimated to be reasonably high, reaching values of 72 and 11, respectively, showcasing its potential for effective CO₂ separation in various applications. Furthermore, Grand Canonical Monte Carlo (GCMC) simulation was conducted to study the adsorption of CO₂ in NS-TMP. Using the isotherm data, performance indicators for a cyclic vacuum swing adsorption (VSA) process were measured to estimate the practical suitability of NS-TMP.